164 
Journal of Agricultural Research voi. ix, No. 6 
leaves than in the green leaves, and the percentage of magnesium is 
almost as great. 
Table V. —Analysis of normal green leaves and of yellow leaves of privet . Collected on 
July j, iqio 
Percentage on dry substance. 
Part analyzed. 
Description. 
Entire leaf. 
Leaf stems of above. 
Yellow leaves. 
Leaf stems of above. 
Yellow leaf margins. 
Green midribs of 
above. 
Leaf stems of above. 
Normal green leaves (entire 
leaf). 
_do.. 
Entire leaf yellow, includ¬ 
ing midrib. t 
... .do... 
Green midrib, yellow leaf 
spread. 
_do... 
_do.... 
Average of yel¬ 
low margins 
and green mid¬ 
ribs. 
Pe. 
Ca. 
Mg. 
PaOs. 
0. 0225 
2.03 
0.250 
0.4S1 
. 0108 
. 844 
• 1 3 1 
.326 
. 0388 
I- 035 
. 196 
1.165 
. 0386 
I* 35 ° 
.174 
. 5 22 
.0312 
. 806 
. 221 
i- 3°5 
. 0242 
1.78 
*259 
.815 
.0197 
•985 
, 148 
.448 
. 0277 
1. 293 
. 240 
I. 060 
SUMMARY 
Previous studies by this office in southern California have shown that 
the percentage of mottling of the Citrus leaves varied inversely with the 
humus content of soils in Citrus groves; that decomposing organic 
matter increases the amounts of soluble salts in the soil; and that a sys¬ 
tem of basin mulching in Citrus groves, especially on certain soil types, 
has produced an improvement in tree growth and fruit setting in com¬ 
parison with the furrow system of irrigation and surface cultivation. 
The purpose of the study here reported was to see if mottled Citrus 
leaves showed a deficiency of the mineral elements directly affecting 
chlorophyll formation. If this were the case, better leaf growth on 
Citrus trees in orchards well supplied with active organic matter might 
be associated with the greater amount of soluble mineral plant food in 
a soil well supplied with decomposing organic matter. 
It was found that orange and lemon leaves very badly mottled con¬ 
tained higher percentages of iron, calcium, magnesium, and phosphoric 
acid than healthy leaves, the average percentage of the entire leaf 
'being considered. 
The leaves in the medium stages of mottling sometimes contained 
more and sometimes less of these elements than healthy leaves. 
In nearly all cases the midribs of the healthy leaves contained less of 
the above-mentioned elements than the mesophyll tissue. In badly 
mottled leaves the midribs contained a higher percentage of calcium 
